In a flat-panel display (hereinafter, referred to as FPD) represented by a liquid crystal display and an organic EL display, a glass substrate is used as the base material of its display panel, but in view of thickness reduction, weight reduction, enhancement of impact resistance and flexibility as well as adaptability to a roll-to-roll process, the demand for replacement by a transparent plastic film is increasing. Also, attempts are being made to form an organic transistor on a plastic substrate by using an organic semiconductor or to form LSI, an Si thin-film solar cell, an organic dye-sensitized solar cell, an organic semiconductor solar cell and the like.
Usually, in the case of forming the above-described device on a commercially available plastic substrate, the device or device formed, such as liquid crystal device, organic EL device, TFT device, semiconductor device and solar cell, is weak to water and/or oxygen and therefore, a dark spot or a dot dropout may be generated during displaying on the display, or a semiconductor device, a solar cell and the like may be prevented from fulfilling their function and cannot withstand the practical use. Accordingly, a gas barrier plastic substrate with a gas barrier performance against water vapor and/or oxygen gas is required. On the other hand, instead of an opaque aluminum foil laminate film, a transparent plastic film provided with a gas barrier performance is hereafter more and more expanding its use in the application as a packaging material for food, medicines, electronic materials, electronic components and the like.
The method for providing a transparent gas barrier performance to a transparent plastic substrate or a transparent plastic film includes a physical film deposition method and a CVD method. Patent Document 1 has proposed a barrier bag film where a gas barrier layer is formed by a plasma enhanced chemical vapor deposition method (PECVD; Plasma Enhanced Chemical Vapor Deposition) using, as the raw material, a mixed gas of hexamethyldisiloxane, 1,1,3,3-tetramethyldisiloxane and/or 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, oxygen, and an inert gas such as helium and argon, but the gas barrier performance thereof is as low as H2O=0.2 to 0.6 g/m2·day and O2=0.4 to 0.5 cc/m2·day.
In Patent Documents 2 and 3, the present inventors have proposed a method for forming a low-dielectric insulating film by PECVD using silane and siloxane compounds each having a structure where a secondary or tertiary hydrocarbon group is directly bonded to a silicon atom. However, these methods are a method for forming a low-density thin film, and the thin film formed is not a high-density thin film suitable for a sealing material, particularly, for a gas barrier material.